A few saffron strands may yellow the water without ending its status as water, so colour change alone does not always prohibit its use.
But if saffron or another substance dominates sufficiently to transform the liquid, it is no longer unrestricted water.
Colour is evidence to consider, not an invariably decisive criterion.
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Unrestricted Water, Restricted Liquids, and Clean Admixtures
A few saffron strands may yellow the water without ending its status as water, so colour change alone does not always prohibit its use.
But if saffron or another substance dominates sufficiently to transform the liquid, it is no longer unrestricted water.
Colour is evidence to consider, not an invariably decisive criterion.